A conjugate “two or pair” cam mechanism is a more practical form of the constant breadth cam mechanism. Conjugate cam mechanisms are designed with two cams on a common shaft. They typically will have two roller followers with one mated tangent to each follower. Typically each roller centers are opposing in a common plane, but there are other designs. That plane will typically intersect the center of the cam shaft, but there are other designs. The two followers are typically rigidly connected to each other to positional encapsulate the two cams. This results in a constant distance between each of the two cam follower rollers. The cam profiles are so designed to cause constant contact with the two rollers. This causes the combined rigid followers to stay in constant contact with the surface profiles of each cam at all moments when the shaft is rotated. This rigid connection of the two followers causes a positive return motion of the followers. That is when one cam is applying displacement it is moving the other follower to its rectilinear direction of displacement “stroke”. This rigid connect of the two follower precludes the requirement for an external force such as spring to keep each follower in constant contact with its mating cam surface profile. Two independent followers and cams with springs could cause the same reciprocating motion imparted to each follower, but it would not be true continuous positive motion over the full 360° of its rotation.
Typically each cam will have its mated follower surface profile contact point 180° apart from the other cam. The shaft typically will rotate (0° to 180° imparting the desired reciprocating rectilinear motion to its one follower. It will also positively move the other follower to the same direction in unison. The second cam will begin to impart its reciprocating rectilinear motion to its follower from (180° to 360/0°). This creates continuous positive motion reciprocating motion in opposing directions. This process is repeated as the conjugate cam mechanism is rotated. A limitation for the conjugate cam design is that the two opposing reciprocating stroke motions must be equal in distance. The invention's follower's motion must be in unison to a given direction for given cam angle of rotation, but it does not have to split the direction of reciprocation over any specific division of cam angle rotation as is common to the state of art of a typical conjugate cam mechanism.
A preferred motion relationship of uniform rotary to uniform reciprocating can be useful in a wide range of machine applications. The state of current art conjugate cam mechanisms cannot create this preferred motion relationship practically as herein described. It would also be desirable to be able to change or modulate the stroke length of the reciprocating motion for any given constant speed of rotation. This is not of common art for conjugate cam mechanism. The invention herein describes a practical conjugate cam design that can create the preferred uniform motion and stroke length modulation. The stroke length modulation version has this ability integral within its design. This can be accomplished with constant positive motion or almost constant positive motion depending on the design of the mechanism. These embodiments are unique combination of desirable motion creations that can be done at high speeds and loads by the invention. There are a limited number of solutions of common art that can create uniform motion, such as modified conjugate heart cams, cylinder cams, and multi-link levers. None are practical at higher speeds of operation and load and all have tolerance issues.
Uniform reciprocating motion is a very desirable motion for a wide range of machines, pumps and other types of mechanical equipment. A cam profile that imparts uniform reciprocating motion has a constant rate of rise and return motion applied to its follower. Theoretically the follower would have virtual constant uniform velocity with zero acceleration. When the follower has acceleration it has theoretically has zero velocity. Uniform motion would theoretically have a velocity that goes from zero to its maximum constant velocity in zero time. To accomplish this, the acceleration would have to be theoretically infinite. The typical design of a cam system that creates uniform motion will prevent infinite acceleration; the values for the acceleration will remain high. The jerk will also theoretically approach infinity. The uniform motion will cause a condition of high acceleration and jerk resulting in a large amount of shock. Uniform motion is therefore seldom if ever used in a cam design if there are significant speed and load requirements. They are typically designed for indexing applications in various types of machines, such as textile machines, winding machines and some pumps.
The common art for creating theoretical uniform reciprocating motion requires a cam profile that visually looks like a heart; it is commonly termed a “heart shaped cam”. The heart shape cam of proper design can virtually convert uniform rotary motion into prescribed theoretical uniform reciprocating motion applied to its cam follower. Heart shaped cams are defined by a sharp reentrant angle and a sharp salient angle each having defined apex points. These defined points are at opposite and equal ends of the cam profile. They will define two equal congruent lengths of the heart shaped cam profile. The two angles will divide the cam profile 180°/180° of cam angle of rotation. Each apex of the two angles will define the point of directional reversal applied to the follower. These two angles define the moment of change in rise to return for the cam follower. These two angles present abrupt motion changes inherent in heart cams. The result is high acceleration and jerk values, which adversely affect follower and linkage life. It will operate with an adverse non-smooth response.
Practical problems are created by both angles of a heart shaped cam. The reentrant angle can have a cam roller radius that cannot keep in constant contact with the cam profile at the reentrant angle. The term of common art is called an undercut region of the reentrant angle portion of the concave cam profile. When this happens the follower roller will have a positional moment with at least two tangents to the cam profile. There is typically no practical size cam follower roller that can sufficiently maintain a continuous single tangent to the heart shaped cam profile across the reentrant cam angle. This is typically solved by designing the cam with wider a reentrant cam angle to allow constant single moment of tangent between the cam profile and its mated follower roller. This will require a modified portion of the heart cams profile that will not prescribe uniform reciprocating motion onto the follower. This eliminates the problem of continuous single tangential relationship to the cam profile through the reentrant angle, but it negates continuous uniform motion on that portion of the cam profile. The roller follower also has an undesirable abrupt angle change at the reentrant angle that lessens a smooth response of motion being applied to the roller follower.
The salient angle and its apex causes a different problem of non-smooth response and it is typically solved by blunting the apex point of the salient angle. This of course eliminates uniform motion being prescribed onto the roller follower. The problem is that at the moment when the axis of the roller following the path of the cam profile is at the apex of the salient angle, the trailing portion of the roller still overhangs a part of the dihedral angle on which moment that the roller has just rolled into its momentary position, and which is necessary to bring the roller into that position. For the axis to continue along the side of the ideal dihedral leading away from the apex, parts of the trailing side of the roller must follow paths, which pass through the substance of the cam inside the dihedral face leading to the apex. The portion of the cam leading to the salient must be present to force the roller axis out to the apex, and must be absent to permit the roller to leave the apex with its axis following the desired path. This among other considerations of design for a heart cam shape that requires the axis of a cam roller moving on the cam will be forced to follow a path with a salient angle with a sharp apex is of impractical design. The reentrant and salient angles and their sharp apex angles are typically designed out of the cam design as to allow for a modified non-continuous uniform reciprocating motion.
Many machines, pumps, combustion engine cam shafts utilize what is termed as a three dimensional cam mechanism. A three dimensional cam has an elongated cam profile along the axis of the cam shaft that allows it to change the prescribed cam angle when moved laterally. The cam is moved laterally to expose a variable cam profile to the follower's roller or sphere. This allows for a dynamic change in the prescribed motion being applied to the follower for any given lateral positional moment. It can be a change in stroke length and or type of motion. They typically are not designed as a conjugate cam to cause continuous positive motion. The three dimensional cam of common art would require a heart cam shape to create uniform reciprocating motion from uniform rotary motion. All of the limitations of such a design as described above would limit the practical application such a design into a three dimensional cam mechanism. The combination of a conjugate design and uniform stroke creation is even more impractical.
As common to the state of art for cam designs the body that is being acted upon by the cam will apply a component of normal force along a line of travel for the follower. This line is typically perpendicular to the center of the follower's roller. There is then a line of action of normal force between the cam profile and the follower. There is an angle between the normal force line and the line of action. This angle is dependent on the tangent between the cam profile and follower roller at the best right angle distance of the angular force to the center of the cam. The state art will typically always apply the line of action as angular force with a distance about the center of its mating cam. This allows any sudden impacts on the follower to apply this sudden force to the line of action. That in turn can be converted to impact torque applied to the cam. This in turn applies it to whatever is creating the applied rotary motion to drive the cam typically a motor. This cause impact stresses to be applied to the complete cam system inclusive of the motor. This cause increased wear and reduced life for any given cam system. In addition a force applied to the follower can create torque applied to cause partial cam rotation.